This invention relates generally to electronic timepieces having an analog display adapted to produce audible signals at preset times, and more particularly to a timepiece including time and calendar computers and a digital display setting system provided with a microprocessor for selectively producing alarm signals, hourly chimes or musical time signatures as well as special birthday or holiday greetings.
In the traditional mechanical clock, the hour and minute hands which turn about the clock face are operated through a gear train driven by a spring motor. When the wind-up clock is of the alarm type, an additional hand is provided that is manually-adjustable to a desired alarm setting, so that when the hour and minute hands reach this setting, an audible alarm is actuated.
Because of inherent mechanical limitations, the setting mechanism of a conventional alarm clock operates inexactly, so that even though the alarm setting hand is positioned, say, at 8:30, the alarm will not be triggered at precisely 8:30 but a few minutes before or after this setting. And because it operates on a scale of 12, a mechanical alarm clock is unable to distinguish between AM and PM, so that if the alarm hand is set at 8:30 and one wishes to be awakened at 8:30 AM, one must be sure to pull out the alarm-enabling button after 8:30 PM to avoid having the alarm go off at this time rather than 8:30 AM.
In recent years, solid state timepieces have been developed which have no moving parts and are capable of displaying in digital terms not only the time but also the date (day and month). One such electronic timepiece is disclosed in U.S. Pat. No. 3,839,856 (1975) to Dargent, whose entire disclosure is incorporated herein by reference.
In an electronic timepiece disclosed in this patent, a high-frequency crystal-controlled oscillator functioning as a time base is coupled through a frequency divider and a display actuator to an electro-optical digital display formed by light emitting diodes (LED). Through the use of large-scale integrated circuit (LSI) techniques, all of the electronic components of the timepiece are fabricated on one or more small silicon chips. Setting is accomplished by actuating either an hour-set or minute-set switch.
In addition to the basic LSI time computer, the Dargent timepiece includes a separate LSI calendar circuit which automatically counts to 30 or 31 days according to the month of the year, except for February when it automatically counts to 29. The calendar circuit makes it possible to display the day and month digitally (say, 2:12 for the 2nd of December).
While a crystal-controlled electronic digital timepiece is far more accurate than a conventional mechanical timepiece, its digital display, whether in LED or liquid crystal (LCD) form, is not as readable as the conventional analog display. Readability, in the sense this term is used in human factors engineering, is unrelated to accuracy. Hence a digital display may be more accurate than an analog display, yet less readable.
The reason for this is that when the hands of a clock indicate, say, six minutes to twelve, what the observer primarily sees is the sector defined by the hour and minute hands. From the size of this sector and its angular orientation and without regard to the dial numbers underlying the hands, the observer perceives that the time is shortly before noon or midnight, for at 12 the hands overlap to extinguish the sector. The equivalent digital display is 11:54, but the significance of this number in terms of how close this time is to noon or midnight requires an intellectual exercise on the part of the observer which is more difficult to carry out than analog perception.
To give a simple example of this distinction: If in order to describe the size of a cat, you hold your hands apart by a distance analogous to the cat size, this give the observer an immediate impression of the physical dimension. If, however, you tell the observer that the cat is 13.55 inches long, though this is more exact, it is more difficult to conceive in actual physical terms.
While a person must be trained or conditioned to tell time in analog terms and the meaning of time expressed in digits is more readily acquired, the fact remains that once one learns to read timekeeping hands, it affords more useful intelligence; for an analog reading not only gives the existing time but also indicates where that time stands with respect to four angular reference or compass points (12, 3, 6 and 9). It is for this reason that aircraft pilots often describe the incoming direction of a plane in terms of analog time--and will say, for instance, that a plane is approaching at 2 o'clock.
Moreover, an analog display, because it it seen in the form of the relatively large sector defined by hands, can be read at a greater distance than a digital display. One can read an analog dial display even though the distance from the display and the lighting conditions are such that the dial numbers cannot be deciphered, whereas one must be close enough to a digital display to be able to discern the numbers.
Hence while modern solid state timepieces in many respects represent a major advance over spring-operated mechanisms having a moving hand display, because of the advantages of an analog display in terms of human factors engineering, many electronic watches and clocks now on the market include a gear train for turning conventional watch hands, the train being driven by a stepping motor actuated by low-frequency timing pulses derived from the time computer included in the timepiece.